Tein Street Advance Z Coilover Kit 2004-2009 Mazda Mazda3 (BK3P)Tein Street Advance Z Coilover Kit 2004 2009 Mazda Mazda3 (BK3P) About the Sealed Structure The top end of the shell pipe is narrowed, oil and gas are injected, and the whole unit is sealed by crimping the metal. This new approach massively shortens the production process. As a result, we have succeeded in vastly cutting production cost. Thread Type Ride Height Adjustment The ride height can be adjusted by moving the lower spring seat up or down.